The present invention relates in general to a random block access memory in which data are randomly accessed in the unit of block, and more particularly to a method and an apparatus for controlling chip extension of the random block access memory.
Generally, a random bit access method of randomly accessing data in a dynamic random access memory (DRAM) or a static random access memory (SRAM) in units of bits has no particular restriction to chip extension of the memory. But, a random block access method of randomly accessing the data in the memory in units of blocks has restrictions to the chip extension of the memory.
FIG. 1 is a block diagram of a conventional chip extended configuration for a random block access memory and FIG. 2 is a memory map showing memory dead zones formed in the conventional chip extended configuration of FIG. 1 by using a conventional block data access technique.
In the conventional chip extended configuration for the random block access memory, as shown in FIG. 1, each of a plurality of extended memory chips 1-3 has an address input terminal AI connected to an address bus of a system, a chip enable signal input terminal CE connected to a chip enable signal input pin of the system, and a data input/output terminal DI/O connected to a data bus of the system.
Upon intending to select a desired one of the memory chips to access it, the system outputs a chip enable signal to the corresponding memory chip. As a result, the memory chip to be accessed is enabled, and data therefrom are accessed according to an address sent over the address bus. The accessed data are outputted to the data bus through the data input/output terminal DI/O.
By the way, the memory dead zones are formed in cells of last edges of the memory chips, as shown in FIG. 2, because the memory chips are accessed by the random block access method. A block start address is limited to a value smaller than or equal to a block size because of the memory dead zones. In other words, dead zones are formed in the cells of the last edges of the memory chips by which a value smaller than or equal to the block size is allowed as an actual start address, whereas a value greater than the block size is disregarded as the actual start address. For example, in the case where the data access is performed in the unit of a 16.times.16 block size, a value (N.ltoreq.16, M.ltoreq.16) smaller than or equal to the block size of 16 is allowed as the actual start address, whereas a value greater than the block size of 16 is disregarded as the actual start address. In this case, the dead zones are formed in the cells of the last edges of the memory chips with address values greater than the block size of 16.
In other words, in the conventional chip extended configuration for the random block access memory, the block is not successive at the boundaries between the adjacent memory chips because of the dead zones. For this reason, after the last accessible block data in the first memory chip is addressed by the first start address, the start accessible block data in the second memory chip must be addressed by the second start address. Namely, the block access cannot be performed successively at the boundaries between the adjacent memory chips because of the dead zones formed in the cells of the last X and Y-direction edges of the first memory chip.